Telecommunications systems, cable television systems and data communication networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical fibers comprise thin strands of glass capable of transmitting the signals over long distances with very low loss.
Optical networks often employ wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM) to increase transmission capacity. In WDM and DWDM networks, a number of optical channels are carried in each fiber at disparate wavelengths. Network capacity is based on the number of wavelengths, or channels, in each fiber and the bandwidth, or size of each of the channels.
Sustaining power levels of optical signals in optical networks presents substantial technical challenges. It is desirable for the power of the signals to be within a dynamic range of the receivers in an optical network, and the dynamic range of the receivers tends to be smaller for higher data rates. Consequently, it is important to employ an accurate method for assessing the necessary level of amplification in the nodes in an optical network.
Due to fast switching speeds required for optical layer protection, optical amplifiers must be capable of quietly accepting the signals and capable of a fast transient response. Since fiber losses may be different for different spans, the gain of an amplifier may need to be determined during span installation and during span recovery after repair of a fiber cut. Moreover, spans with no provisioned or active wavelengths will need to operate normally after wavelengths are switched to such spans due to optical layer switching.